Define m171 as the integer whose little-endian representation is
m followed by 1 if m has at most 171 bytes,
or the first 171 bytes of m followed by 1 if m has more than 171 bytes.

Finally, define H0(r,m) as
(h[0] + 2^32 h[1] + 2^64 h[2] + ... + 2^1504 h[47]) xor (2^160 m171).
This is in {0,1,2,...,2^1536-1};
it cannot be 0,
because if h[0],h[1],h[2],h[3],h[4] are all 0
then h[37] has top byte 101.